The overall objectives of this research project are to elucidate the role of repetitive DNA sequences and haploid DNA content in the evolution of the genome in plants. Since there are three genomes in plant cells - nuclear, chloroplast (ct) and mitochondial (mt) - we would like to know whether all three evolve in a similar manner or whether they evolve independently of each other. We are beginning to gain some perspective in this matter and have obtained some very interesting information on these three genomes, especially the mitochondrial. In the coming year we plan to conclude our analysis of chloroplast DNA and concentrate on the analysis of repeated sequences in mitochondrial DNA. We also will continue to investigate the perplexing issues of the large and variable nuclear DNA content among some closely related species. For four species in the cucumber family we have found the sequence complexity of mtDNA to be from 25 to 135 times that for mtDNA in metazoan animals. We plan to look outside the cucumber family at pea and corn and also to examine the small amount of repetitive DNA present in the cucurbit mtDNAs.